LECT. VIII.] STRUCTURE OF HERBACEOUS ROOTS. 439 



and its place is supplied by a new one ; but in 

 this plant the cellular matter, which is found 

 situated immediately under the cuticle in the 

 young*, is deficient in the old root. 



The transverse section of the root of Marsh 

 Mallow, Althaea officinalis, displays a kind of 

 pith composed of one large fasciculus of sap vessels 

 in the centre, surrounded by a mass of cells ar- 

 ranged in rays, having a few small fasciculi of sap 

 vessels dispersed through it; and several larger 

 on its verge, forming an interrupted circle round 

 it. The cortex is thick, cellular, and contains clus- 

 ters of proper vessels arranged in a radiated form* 

 In the longitudinal section we find that the sap 

 vessels are punctuated, but not spiral; and the 

 tubular cells are comparatively much shorter and 

 wider than those in the root of Dandelion ; a cir- 

 cumstance which appears almost to be essential, 

 when we consider the nature of the mucilaginous 

 secretion deposited in them. 



In both these roots the central part readily se- 

 parates from the cortex; and, except in very 

 young roots, it is from the latter only that we can 

 extract the secretions on which their value as me- 

 dicinal agents depends. 



2. Perennial herbaceous roots composed chiefly 

 of common cellular matter. The root of Deadly 

 Nightshade, Atropa Belladonna, may be taken as 



FF4 



